$trans
  transition transform .2s ease

$size = 30px

.sider-trigger-a
  padding 6px
  width $size
  height $size
  display inline-block
  text-align center
  color #5c6b77
  margin-top 16px
  background #19be6b
  color white
  border-radius 4px
  &:hover
    color white
    opacity .8
  i
    @extend $trans
    vertical-align top
  &.collapsed i
    transform rotateZ(90deg)
    @extend $trans
